Future motor vehicles will likely have a different system structure than is common today. Production of electric power will likely be carried out by one or more generators which, in addition to being driven by an internal combustion engine, will also receive a supply of mechanical energy resulting from braking operations. This method, already known as braking energy recovery, makes it necessary to a still greater extent than in the standard case today of the generation of electrical energy to have generators and electrical storage media which are designed for considerably higher proportion of peak currents which are needed or provided.
Since, however, weight limits relating to the presence of a generator and a battery have to be complied with in each vehicle in order to avoid forfeiting the advantage of more efficient power generation and the associated lower fuel consumption because of an increase in vehicle mass, it is necessary to use particularly efficient components.
Within the context of the technical implementation of energy management systems for motor vehicle systems, an extremely wide range of methods for monitoring, in particular, the state of charge of the storage batteries are known.
For example, in a method of measuring the state of charge, DE-C 2242510 discloses the practice of weighting the charging current with a factor that depends on the temperature and on the state of charge of the battery itself.
DE-A 4007883 discloses a method in which the starting capacity of an accumulator is determined by measuring accumulator voltage and battery temperature and comparing with a family of curves of the state of charge which apply to the battery type to be tested.
DE-A 19543874 discloses a calculation method for the discharge characteristics and residual capacity measurement of a battery, in which likewise, current, voltage and temperature are measured, the discharge characteristics being approximated by means of a mathematical function with a curved surface.
DE-C 3901680 describes a method of monitoring the cold-start capability of a starter battery in which the starter battery is loaded from time to time with a resistance, the voltage which drops across the resistance is measured and, in a comparison with empirical values, is used to determine whether the cold-start capability of the battery is still adequate. In this case, the starting operation is used to load the starter battery.
Finally, DE-A 4339568 discloses a method of determining the state of charge of a motor vehicle starter battery in which battery current and quiescent voltage are measured and used to determine the state of charge, the battery temperature also being taken into account. In this case, the charging currents measured during different time periods are compared with one another and used to determine a residual capacity.
However, the aforementioned battery monitoring methods, whose information is at the same time a basic precondition for the specific management of the electrical energy in the vehicle electrical system, still do not contain approaches to the implementation of this control intervention required for more efficient fuel utilization.
It would, therefore, be advantageous to provide defining an energy management system and, with the aid of this system to influence the generation, consumption and storage of electrical energy in such a way that overall vehicle efficiency is improved. In addition to technical limitations, it is necessary to make “energy” decisions such that the safety of motor vehicle passengers is not restricted or compromised and vehicle comfort does not appreciably decrease.